Electronic motor control circuit



1953 o. E. SAWYER ET AL ELECTRONIC MOTOR CONTROL CIRCUIT 2 SHEETS--SHEET1 Filed Feb. 7, 1946 III gwue/wkw OGDEN E. SAWYER HENRY R. WARREN Feb.1953 o. E. SAWYER ET AL 2,627,594

ELECTRONIC MOTOR CONTROL CIRCUIT Filed Feb. 7, 1946 2 SHEETSSHEET 2 so I59 FIG. 2

OGDEN E. SAWYER HENRY R. WARREN Patented Feb. 3, 1953 UNITED STATESOgden E. Sawyer, Cranston, R. 1., and Henry R. Warren, Louisville, Ky.,assignors to the United States of America as represented by theSecretary of the Navy RATENT OFFICE Application February '7, 1946,Serial No. 646,164

1 Claim. 1

The present invention relates to electronic motor control systems andmore particularly to an alternating current control circuit employingthermionic tubes for controlling the operation of a split field motor.

It is often desirable to control with precision from a remote stationthe speed and direction of rotation of a motor and to effect the motorcontrol by the application of a relatively small amount of signal orcontrol energy. The present invention is well suited for this purpose,and is particularly adapted for use in servo systems employed, forexample, to control the movement of repeaters and similar equipment ingyro-compass systems, of transducers in underwater sound systems, ofarmament in fire control systems and of antenna in radar systems. Thecontrol signal employed in the present invention may be variable inmagnitude and is derived from a phase shifting means such as aninduction or electrostatic device, a phase shifting network or anelectronic means, which serves to translate the movement of thecontrolling instrumentality into a potential having a variable phaserelation with respect to the energizing source.

An. object of this invention is to provide an improved electroniccontrol system by which the direction and speed of a split field motorcan be controlled with precision in accordance with the phasing of anapplied signal potential.

Another object of the invention is to provide an improved electroniccontrol circuit for a split field motor whereby the phase relationshipof the energizing potential serves to control the braking torquedeveloped by the motor.

Another object of the invention is to provide an improved electroniccontrol circuit by which a motor is energized with the A. C. componentof the rectified alternating current provided by the control circuit,

The invention also resides in certain novel features of circuitarrangement which facilitates the carrying out of the foregoing objectsand which contribute both to the simplicity of the electronic controlcircuit and to the reliability of its operation to control the directionand speed of a split field motor upon the occurrence of a properlyphased signal potential and to enable the motorto develop a high brakingtorque which brings the rotor to a quick stop upon the cessation of thesignal or control potential.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawing, in which? Figure 1 is a circuit diagram showing apreferred arrangement of the invention,

Figure 2 comprises a group of curves which illustrate the phaserelationship of the cathode and anode voltages under non-operating andoperating conditions of the circuit disclosed in Figure l and Figure 3is a circuit diagram showing an alternative arrangement of a part of thecircuit disclosed in Figure 1.

While the invention is susceptible of various modifications andalternative arrangements, we have shown in the drawings and will hereindescribe in detail the preferred embodiments. It is to be understood,however, that we do not intend to limit the invention by such disclosurefor we aim to cover all modifications and alternative arrangementsfalling within the spirit and scope of the inventions as defined in theappended claim.

Referring to Figure 1, reference numeral I0 represents a split fieldmotor, the direction of rotation and speed of which is controlled by thecharacteristics of the signal potential impressed upon the controlcircuit as will be hereinafter described. For purposes of thisdescription motor l-Q will be ccnsidered as being of the two-phasealternating current induction type employing a squirrel cage type rotoralthough it will be apparent that other types of split field motors maybe used without departing from the spirit of the invention. Motor it isrovided with two stator windings I! and II! which are connected togetherat a common terminal 13 and are spaced 90 degrees electrically from eachother. The voltages impressed upon each of the stator windings must beapproximately 90 degrees out of phase, which phase difference combinedwith the effect of the 90 degrees mechanical spacing of the windingsresults in a rotating magnetic field which induces a voltage in therotor by transformer action. A rotating torque is produced by theinteraction of the magnetic fields thus established.

The stator winding I! and H! are energized by the control circuit in amanner to result in the desired direction of rotation and speed of therotor i2 in accordance with the phase of a signal or control potentialimpressed upon the primary winding M of input transformer 15. Each endterminal ll and E8 of secondary winding [6 of input transformer i5 isconnected to the grid of a thermionic device as is shown in Figure 1.End terminal H is connected to discharge device 20 by conductor 2! andend terminal 18 is connected to the grid of discharge device I byconductor I2I. The thermionic devices 20 and I2!) are preferably of thegaseous discharge type represented by gas triode tubes known as'Ihyratrons having a cathode, controlled grid and anode. It will beapparent to those skilled in the art that other types of discharge tubescould successfully be employed in the circuit with slight modificationof circuit constants.

Grid-current-limiting resistor 22 is connected in series in conductor ZIbetween the grid of tube as and end terminal, I! and current-limitingresistor I22 is connected in series in conductor I2I between the grid oftube I 20 and end terminal IS. A grid-biasing voltage is supplied to thetubes by a transformer 23 through a phaseshift network 29 consisting ofa shunt resistor 24 and a capacitor 25 in series with the secondarywinding of transformer 23. 0ne side of the shunt resistor 2 is connectedto a common cathode terminal 26 by conductor 2'! and the other side isconnected to the center tap 23 of secondary winding I3 of inputtransformer I5. C'ommon cathode terminal 26 is connected to the cathodeof tube "2D and tube I 23 by conductor 39. Bypass circuits are providedto prevent high frequency voltages from reaching the grids of dischargedevices 20 and I23 which comprise capacitors 3i and I39 and resistors 3Iand I3I.

Capacitor 33 and resistor 3| are connected in series between conductor2I and conductor 2? which is connected to the common cathode terminal 28and capacitor I30 and resistor I3I are connected between conductor I2Iand conductor 27.

The plate potential for tubes 29 and I29 is provided through platesupply transformer 34 which has a primary winding 35 and a secondarywinding 33. One end terminal of the secondary winding 36 is connected tothe common cathode terminal 26 and the other end terminal of secondarywinding 36, identified by reference numberal 37, is

connected to the respective plates of discharge devices 23 and i 23through choke coil 38 and I38. The plates of the gaseous dischargedevices 20 and I26 are also connected to the stator termirials of thetwo-phase alternating current induction motor It. The plate of tube 20is connected toend terminal 62 of stator winding Ii through capacitor 9and the plate of tube I23 is connected to end terminal I 32 of statorwinding III through capacitor it. The common terminal I3 to which theopposite ends of the stator winding-s II and II! are connected, isconnected to the terminal 31 of the secondary winding 35 r the mannercommonly adapted for producing 1 leading current in one winding of atwo-phase induction motor, between the stator winding terminals 32 andI32.

The circuit shown in Figure 1 operates in the following manner when nosignal voltage is im pressed upon the primary winding of inputtransformer I5 and when transformers 23 and 34 are energized from asuitable source of power. The anodes of tubes 23 and E23 are madealternately positive and negative with respect to the cathodes by thealternating current potential supplied through plate transformer At thesame time the grids of tubes 2c and i2 3 are made alternately positiveand negative by the biasing voltage delivered by transformer 23 throughthe phase shift network 29. However, the grid biasing voltage is made tolag the plate voltage a susbtantial num plate-voltage cycle.

4 her of degrees by the phase shift network 29. The specific phasedifierence is not critical as long as the voltage lag is in the vicinityof degrees.

The relationship of the anode voltage and the grid-biasing voltageexisting in one side of the circuit during a cycle of operation is shownby the curves of Figure 2 with reference to the critical grid-bias belowwhich the tube cannot conduct. Curve 50 represents the plate voltage,curve 5| represents the grid-biasing potential andrcurve 52 representsthe negative grid voltage necessary to prevent current flow in the anodecircuit during the positive half of the From curves 5| and 52 it will benoted that the negative grid-biasing voltage drops below the limitingvalue at the point of intersection 53 of the two curves, thusintitiating the flow of anode current, which continues to the end of thepositive half of the anode voltage cycle. This current flow isrepresented by the shaded area 56 in Figure 2. a

. Since current can flow in the plate circuit only during the positivehalf of the plate-voltage cycle, it takes the form of pulsating directcurrent, or a direct current with a superimposed alternating current.through the motor windings II and .I II serves no useful purpose andacts adversely by reducing speed and torque and by causing heating ofthe To prevent this flow, the chokecoils.

windings. 38 and I38 and capacitors ell and I40 are provided in thecircuit. The direct current component passes through thechoke coils,while, the alternating current component passes through the capacitorsto the motor windings. As both tubes 20 and I2!) become conductivesimultaneously, the alternating current components entering the motorwindings II and III are in.

phase and equal in magnitude and no torque is produced in the rotor I2due to the bucking accuit, it will be assumed that when a signal po-.tential is applied to the primary winding I4 of input transformer I3, avoltageis-produced in the half of the secondary winding I6 connectedthrough current-limiting .resistor 22 to the grid of tube 26. This.volta'gewhich is. represented by curve 55 in Figure 2combines-algebraically with the, grid-biasing voltage -5I to produce aresultant voltage .56 which isapplied to the grid of tube 20. I55combined. with the grid-biasingv voltage'to produce-a resultant voltage57 which is applied to the grid of tube 420..

As the instantaneous value of a signal voltage{ 55- increases during-ahalf cycle, the time-point of intersection 58. of the resultant voltagecurve 56 with the limiting curve 52, andhence the timev of initiation ofplate-current flow in the tube 20,

rapidly becomes earlier than that represented by intersection 53 untilthe condition shown in l gure 2 v is; reached,- in, which theplate-current i flowing during practically hali ofthe entire- Directcurrent flowing Simultaneously .the' signal voltage positive half of thecycle as represented by the shaded area 59. Further increase in thesignal voltage 55 would shift the point 58 to a still earlier positionuntil, for a certain value, the plate-current Would fiow duringsubstantially the entire positive half cycle. Simultaneously, the point6| becomes later, reducing the time during which the plate-current flowsin tube I to practically nothing, which condition is represented by theshaded area 60. Thus the flow of bucking current in the winding isreduced to a minimum during the half cycle.

The pulsating plate-current flowing through tube 20 is separated by thechoke coil 38 and oapacitor 40 into direct and alternating-currentcomponent and the alternating-current component is applied to terminals42 and I 3. Thus current will fiow directly through the field windingll, while the phase-splitting capacitor 44 produces a leading currentthrough the field winding III. The action of the current through the twofield windings results in a rotating field which produces a torque inthe rotor I2 to cause it to rotate in a selected direction.

If the polarity of the incoming signal is reversed, tube [20 becomesconductive and current will flow directly through the field winding IIIwhile the phase-splitting capacitor will produce a leading currentthrough the winding ll. Thus the action of the currents in the twofields will cause the rotor [2 to rotate in the opposite direction.

Upon cessation of the incoming signal, both tubes 20 and I20 becomesimultaneously conductive over a short portion of the cycle ashereinbefore described and since the currents supplied to both fieldwindings of the motor is in phase, a high braking torque is developeddue to the bucking efiect of the fields which serves to bring the rotorto a quick stop.

The alternative arrangement disclosed in Figure 3 provides an increaseof sensitivity of the motor control circuit by terminating theconduction of the late-firing tube more quickly as the signal or controlpotential increases during a cycle. This action decreases the buckingcurrent still further through the motor windings and thereby serves toincrease the torque produced. The circuit shown in Figure 3 is similarto the circuit of Figure 1 except that instead of connecting thecathodes of the tubes 20 and I2!) directly to conductor 2'! between thesecondary windings of transformers 23 and 34, the cathodes are connectedby conductor 39 to conductor 2'! through a resistor 54 which is shuntedby capacitor 55. When neither of the tubes is conductive, conductor 39is at the same potential as conductor 21 and when no signal potential isbeing impressed on the primary I4 of input transformer l5 both tubessimultaneously conduct briefly just before the end of the cycle. As hasbeen explained with reference to Figure 1, when a signal potential isimpressed on transformer [5, one of the tubes is caused to fire orbecome inductive ahead of the order. The resistor 64 forms part of thecircuit through which the plate-current flows. In consequence, as theincoming signal potential increases in value, the potential of theconductor 39, and with it that of the cathode of the unfired tube, isgradually raised with respect to the potential of conductor 2! to apositive value which soon becomes greater than the positive value of theincoming signal which produces a condition whereby the tube ceases to beconductive. Thus, for a given signal potential, less bucking current isproduced in the motor windings, and the torque output of the motor ishigher than it would be with the resistor out of the circuit.

The capacitor 65 is provided to by-pass the alternating currentcomponent of the pulsating direct current resulting from the half waverectifying action of the tube. In this manner a greater alternatingcurrent voltage is provided across the field windings of the motor. Thecapacitor 65 also serves to maintain the potential difference orpositive bias as the end of the half cycle is approached.

We claim:

In a system for controlling the speed and direction of rotation of amotor, an alternating current motor having two primary windings hav inga pair of end terminals and a common terminal, a pair of thermionictubes each having a cathode, an anode, and a control grid, a pair ofinductances each having one terminal connected to a respective one ofsaid anodes of said thermionic tubes respectively and one terminalconnected to a common power terminal, a first source of alternatingcurrent connected to the cathodes of said thermionic tubes and to saidcommon power terminal for energizing said anodes through saidinductances, an alternating current signal voltage varying in phase andamplitude with the desired direction and speed of rotation of said motorrespectively, centertapped means for impressing said signal voltage inphase opposition on said grids respectively a second source ofalternating current lagging said first source of alternating current bymore than ninety electrical degrees impressed on said grids in phasewith each other, capacitive means connecting said end terminals of saidmotor to said anodes respectively, means connecting said common powerterminal to said common terminal of said motor, and a capacitanceconnected to said end terminals of said motor, whereby the speed anddirection of said motor is determined by the phase and amplitude of saidalternating current signal voltage.

OGDEN E. SAWYER. HENRY R. WARREN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,955,322 Brown Apr. 17, 19342,054,945 Nisbet Sept. 22, 1936 2,164,728 Wey July 4, 1939 2,209,369Wills July 30, 1940 2,389,827 Stein Nov. 27, 1945 2,414,384 Moseley Jan.14, 1947 2,417,868 Glass Mar. 25, 1947 2,508,639 Field May 23, 1950

